It is known that numerous parts of aircraft are now made of composite materials, particularly materials based on carbon fiber, and that in order to avoid these composite parts being destroyed, or at least damaged, in the event of lightning, electricity conducting means are provided for dissipating the energy of the lightning. Such electrically conducting means are generally conducting layers, for example made of metal mesh, latticework or fabric, arranged on the surface of said composite parts. Thus, the known spark-resistant structures, particularly for aircraft, generally comprise:
an external element, in the form of a sheet, made of a composite material and having an exterior face bearing an electrically conducting surface layer for dissipating lightning energy, and an interior face; PA1 an internal element in the form of a sheet having an exterior face and an interior face, said external and internal elements being arranged in such a way that the interior face of the external element is at least partially superposed with the exterior face of said internal element, and being provided with holes which are aligned opposite each other; and PA1 fixing means passing through said aligned holes opposite each other and forming an alignment of fixing means for holding said elements together in a fixed position, said fixing means being electrically in contact with said conducting surface layer, for example by means of amounts of electrically conducting paste introduced into said holes of said external element, as described in document EP-A-0248122. PA1 in that said external element comprises, under said conducting surface layer, an electrically conducting strip extending longitudinally in the direction of said alignment of the fixing means, through which strip said fixing means pass, and which is in electrical contact with said means; and PA1 in that the electrical contact between each of said fixing means and said conducting strip is obtained by means of said amount of electrically conducting paste introduced into the hole in said external element through which said fixing means passes.
Thus, when lightning strikes said fixing means (metallic screws or rivets for example) the lightning current is transmitted to said electrically conducting surface layer, where it dissipates.
However, dissipation of energy of this kind assumes that there is good electrical contact between said fixing means and said conducting surface layer, because otherwise the lightning current causes damage to the structure, in the region of said fixing means and said internal and external elements. So, to ensure satisfactory electrical contact between the fixing means and said conducting surface layer, provision has already been made for the interposition of electrically conducting washers, for example made of foil, associated with each of said fixing means and whose task is to make sure that these fixing means make electrical contact with said surface conducting layer. However, the fitting and fixing of these washers are difficult, lengthy and complex operations which are further complicated by the fact that, in order for the exterior surface of the surface to be smooth, it is usual for said fixing means to have a countersunk head housed in countersinks made in the exterior face of said external element.